In accordance with the known prior art methods for producing artificial leatherlike materials, it is known to produce an artificial leather composite material by casting of a polymer solution onto a transfer paper to produce a simulated leather facing layer of the composite. The transfer paper is specially prepared by embossing of a paper sheet material with a negative configuration of the fissures and ridges of a simulated leather texture and by treating the embossed surface of the paper sheet material with an appropriate release agent. The release agent-treated embossed surface of the transfer paper material is coated with an organic solution of the polymeric material and the solvent fraction then driven off from the cast solution by conducting the coated transfer paper through one or more drying ovens. In general, in order to achieve the desired final thickness the preparation of a cast simulated leather facing layer of the composite is usually undertaken as a plurality of solvent based polymer coatings onto the transfer paper surface, following each of which coatings the solvent phase of the cast polymer solution is removed. Once a simulated leather facing layer of the desired thickness has been produced by such solvent coating technique the resulting leather grained facing layer is stripped from the transfer paper and is continuously bonded to a flexible backing material such as, for instance, a paper substrate layer such as cardboard or tagboard or to a layer of a woven (including knitted) or nonwoven fabric, said backing material layer serving to confer structural integrity to the overall artificial leather composite material.
One of problems attendant the preparation of artificial leather composite materials involving the solvent based coating of polymers onto embossed transfer papers broadly resides in the environmental, pollution and toxicological considerations inherently involved in the handling of large quantities of organic solvents. Once the polymer solution is cast onto the embossed transfer paper surface it is, of course, necessary to then safely and completely remove the organic solvent from the so deposited polymer solution and, to the extent possible, to recover the solvent fraction therefrom. While the solvent recovery schemes conventionally utilized in the art are generally effective, they do not usually result in complete recovery of the solvent fraction. Thus, in order to avoid atmospheric pollution, it is usually necessary to yet further treat the atmospheric overhead of the solvent recovery zone before releasing it into the atmosphere, such as by high temperature incineration of said overhead. Accordingly, it will be appreciated that the handling of the solvent fractions of the polymer solutions utilized in the preparation of cast simulated leather facing layers is capital intensive in terms of solvent recovery and pollution control equipment and constitutes a substantial expense in the overall cost of production.
Additionally, the polymeric coating solutions employed in the preparation of cast simulated leather facing layers comprise no more than about 50% by weight polymer solids and, more often, no more than about 30% by weight polymer solids. Accordingly, it is difficult and, in many instances, impossible, to attain the desired finished thickness of the grained texture simulated leather facing layer on the basis of a single coating step and, as was indicated above, cast leather grained facing layers of the desired thickness are usually producible only after plural castings of the polymer solution onto the transfer paper have been achieved. After each coating step it is, of course, then necessary to remove, recover or otherwise deal with a substantial solvent fraction from the deposited wet polymer coating. Moreover, the exposure of the relatively expensive release agent-treated embossed transfer paper component of the casting process to the solvent or carrier liquid phase of the polymer solution and the relatively lengthy times to which the transfer paper is exposed, particularly in the presence of the solvent fraction, to the elevated temperatures existing within the drying oven(s) adversely affects its service life.
Yet another problem often experienced in the applications to which such solvent cast artificial leather composite materials are put resides in the problem of "read through" whereby the weave or fibrous nature of the backing layer of the composite and/or the substrate surface to which is is applied tends to be physically expressed through the leather grained surface of the facing layer to which it is adhesively bonded. This cosmetically unattractive phenomenon typically occurs during the course of (a) adhesive bonding of the backing layer to the cast facing layer wherein pressure is brought to bear on the assembled composite at elevated or ambient temperatures, and/or (b) physical stressing of the artificial leather composite material, such as by bending and/or adhesively securing it around a contour of a fixed substrate surface, such as an outside contour of a frame of a briefcase or the last of the heel or toe of a shoe.
In accordance with the present invention the above problems have either been entirely avoided or, in the alternative, have been substantially ameliorated.